The present invention relates to resinous star-block copolymers having improved impact properties and good clarity.
Highly branched block copolymers, sometimes called star-block copolymers, are old in the art of anionic polymerization. These star-block copolymers are prepared by first forming linear block polymers having active lithium atom on one end of the polymer chain. These active, linear polymer chains are then coupled by the addition of a polyfunctional compound having at least three reactive sites capable of reacting with the carbon to lithium bond on the polymer chains to add the polymer chain onto the functional groups of the compound.
Zelinski, U.S. Pat. No. 3,280,084, polymerized butadiene with butyllithium initiator to form B-Li blocks (where B is polybutadiene) which when coupled with divinylbenzene gave highly branched copolymers having polydivinylbenzene nuclei and several identical arms of polybutadiene branching therefrom. The arms can also be either random or block copolymers of styrene and butadiene (from A-B-Li blocks, where A is polystyrene segment) where the diene is the major component.
Childers, U.S. Pat. No. 3,637,554, prepares rubbery star-block copolymers having nuclei formed from polyepoxides, polyisocyanates, polyimines, etc., and identical arms from B-Li and A-B-Li.
Kitchen et al, U.S. Pat. No. 3,639,517, teaches that star-block copolymer may be formed having different molecular weight arms attached to the same nucleus. These arms are formed by using multiple additions of styrene monomer and initiator to form A-Li; A'-Li; and A''-Li, where A, A' and A'' are polystyrene blocks of different molecular weights, then by a single addition of butadiene, and finally coupling these arms to form star-block copolymers having bi-, tri-, and polymodal molecular weight distribution in the arms.
Fetters et al, U.S. Pat. No. 3,985,830, discloses a product having at least two star-block copolymers linked together by a linking agent, such as phosgene, silicon tetrachloride or dihalosilanes.
Fodor, U.S. Pat. No. 4,051,197, discloses blends of two star-block copolymers, each having molecular weight distribution in its arms outside a given range, to form a blend having a distribution within the given range.
Fahrback et al, U.S. Pat. No. 4,086,298, discloses star-block copolymers having a mixture of arms wherein some are formed by first polymerizing styrene with alkyllithium to form A-Li blocks, and then adding a mixture of styrene and butadiene to form a graded copolymer represented by A-B.fwdarw.A', where the arrow represents a graded segment. Other arms are made up on only the butadiene-styrene graded copolymer segment.
Kitchen, U.S. Pat. No. 4,091,053, teaches that star-block copolymers having long integral hinge flex life and high hardness can be made by the method of U.S. Pat. No. 3,639,517 wherein the ratio of molecular weight of the styrene blocks in a longer (A') block to that of a shorter (A) block is maintained within the range of 3 to 7.
Vreugdenhil, U.S. Pat. No. 4,092,375, makes the bimodal star-block copolymers of Kitchen, U.S. Pat. No. 3,639,517, by separately preparing blocks of A-B-Li and B-Li, and then coupling mixtures thereof.